Little is known about the precise mechanism of loading of peptides derived from HIV-1 onto MHC-II molecules expressed by antigen presenting cells (APC). This loading of HIV specific peptide on MHC-II molecules is essential for the activation of both na[unreadable]ve and specific CD4+ T cells. It must occur because CD4- T cell responses can be demonstrated in some HIV-infected persons, and CD4+ T cell help is required to generate the anti-HIV humoral immune responses observed in patients. [unreadable] [unreadable] Hypothesis: 1. That HIV enters APC through a combination of specific receptor mediated mechanisms and nonspecific mechanisms some of which lead to rapid presentation of HIV peptides on MHC-II before productive infection occurs. 2. That different forms of HIV (HIV-1 virions, live or apoptotic HIV-infected cells, and HIV-containing exosomes) are presented on MHC-II with different efficiencies. Specific Aim 1. To determine the mechanism(s) used by APC to internalize and process HIV-1 for presentation on MHC-II molecules. HLA-DR restricted T cell hybridomas that recognize HIV antigens presented by human DC and macrophages will be used. T cell hybridomas serve as a bioassay for specific peptide:MHC complexes. This system will allow the use antibody and pharmacologic inhibitors to study the mechanisms of uptake, processing, and presentation of HIV-1. These studies will be performed in monocyte derived DC, monocyte derived macrophages, primary blood myeloid and plasmacytoid DC, and primary DC and macrophages from colonic and cervicovaginal mucosa. Quantitative analysis of intracellular trafficking of HIV in DC will be performed by high-resolution microscopy. Specific Aim 2. To determine the form of HIV-1 or HIV-1 antigen most efficiently processed and presented by MHC-II molecules. MHC-II antigen presentation of HIV-1 virions, HIV infected cells (live and apoptotic), and HIV-containing exosomes will be studied in human monocyte derived and primary APC. [unreadable] [unreadable] A better understanding of MHC-II antigen presentation of HIV-1 will aid in understanding events early [unreadable] in infection when CD4+ T cells are primed and the character of CTL and B cell responses is being [unreadable] determined by the quality of CD4+ T cell help they receive. A better understanding of the optimal forms of HIV antigen for presentation will aid in vaccine design and development. Knowledge gained may help aid in developing strategies to modulate HIV infection in APC to bias toward degradative pathways and not those that result in productive infection or trans-infection of CD4+ T cells. [unreadable] [unreadable] [unreadable] [unreadable]